1. Field of the Invention
The present invention relates to computer-enabled length calculating systems and methods, and particularly to a system and method for calculating circuit trace lengths of a printed circuit board (PCB) layout.
2. Background of the Invention
Computer chip sizes are continuing to be miniaturized, and electrical signals are being clocked at ever increasing frequencies. Even more that previously, high-speed, high-frequency signals being driven between chips via traces on a PCB are liable to detrimental impedance effects. One manifestation of these impedance effects is unwanted reflections due to impedance mismatches. The high-speed, high-frequency signals may also be prone to cross-talk and electromagnetic interference (EMI).
EMI is an electrical disturbance in an electronics-based system. EMI can be caused by natural phenomena such as lightning, by low-frequency waves emitted from electromechanical devices such as motors, or by high-frequency waves emitted from integrated circuits and other electronic devices such as routers. In the United States, the Federal Communications Commission sets limits on the EMI output of electronic devices. Other countries set their own limits on the EMI output of electronic devices. It is therefore necessary for all parties involved in the fabrication, manufacture, and/or sale of electronic devices to comply with the limitations imposed. In particular, it is necessary for manufactures to ensure that EMI emissions of electronic devices are at or below the maximums imposed in particular jurisdictions.
The length of each trace on a PCB is a parameter affecting EMI emissions. Generally, the EMI emission is directly proportional to the length of the trace. Therefore, when constructing a PCB layout, it is necessary to calculate the length of each trace to insure that the EMI emissions caused by the traces meet the requirements imposed in the relevant jurisdiction(s). Additionally, such calculation should be performed before the final physical layout of the PCB is determined, in order to avoid or minimize the difficult and expensive process of rectifying improper lengths.
Accordingly, there is a need for an inexpensive system and method for calculating trace lengths of a PCB layout, in which calculation is fast and can be performed as early as possible in the design process.